The concept is that you've (say) 32 ammo, and each one lasts 30 seconds. This time, it probably does half damage of the cruise missile. Plan on using the model for the MRL as the carrier and the projectiles for it (probably) as the projectiles. Guidance would be the same as the normal Black Plague, though.
On another (unrelated) topic, anyone know where one can download the weird-looking gold powerup that included "Cruisin' for a Bruisin'" and several other random weapons? Have had a request from a friend who connects to my server to find and get it back available. Also: Have a weird problem that happens quite frequently. I get a powerup at a gate (have only noticed this during races) that is a twisty spiral. When you hit it, it morphs into something random, but usually a stock weapon. Very weird stuff. (Also possible to make it pop up the weapon without collecting it, but that's tricky, unless you already have a bolt-on.)